The invention relates to a data carrier with a first circuit. The data carrier has a coil connected to the first circuit through a contactless interface. The contactless interface obtains, from a signal induced in the coil, at least one DC supply voltage, a clock signal, and a data signal corresponding to a modulation of the induced signal, and with a number of contacts connected to the first circuit for receiving at least one supply voltage, a clock signal, and a data signal. The supply-voltage contact is connected to the first circuit through a switching element.
A data carrier is disclosed in International PCT publication WO 96/38814. That data carrier is configured as a chip card, more precisely, as a combination chip card. Data carriers according to the invention can, however, also be realized with different forms of housing. In the case of the prior art data carrier, a diode is disposed between the supply-voltage contact and a logic circuit with such a polarity that it prevents the DC supply voltage present at the output of the rectifier of the contactless interface, likewise connected to the same supply voltage input of the logic circuit, from punching through to the contact. However, such a diode requires a certain minimum voltage in order for it to conduct at all and has, in the forward mode, a voltage drop having a disruptive effect if a low supply voltage is desired.
German Published, Non-Prosecuted Patent Application DE 195 31 372 A1 discloses a chip card suitable for operation with and without contacts. A switch is provided that makes it possible for a voltage at the supply contact to be switched through to a memory in a manner depending only on the state of a control signal of a microprocessor, otherwise the switch connects it for contactless operation. In the case of the chip card, the switch also prevents operation of the microprocessor from the contactless interface.
It is accordingly an object of the invention to provide a data carrier for operation with and without contacts that overcomes the hereinafore-mentioned disadvantages of the heretofore-known devices of this general type and that prevents a voltage induced in the coil at the supply voltage contact and has no appreciable voltage drop in the forward mode at a blocking element bringing this about. In addition, the data carrier ensures access to a microprocessor with and without contacts with equal authorization in terms of the circuitry provided.
With the foregoing and other objects in view, there is provided, in accordance with the invention, a data carrier including a first logic circuit, a contactless interface circuit, at least one coil in which a signal is induced, the at least one coil connected to the first logic circuit through the contactless interface circuit, the contactless interface circuit obtaining from the induced signal at least one DC supply voltage, a clock signal and a data signal corresponding to a modulation of the induced signal, a controllable switching element having a control input, contacts for receiving the at least one DC supply voltage, the clock signal, and the data signal, the contacts being connected to the first logic circuit and having at least one supply-voltage contact receiving the at least one DC supply voltage and a clock-signal contact receiving the clock signal, the at least one supply-voltage contact being connected to the first logic circuit through the switching element, and a second logic circuit having an input side and an output side, the input side connected to the clock-signal contact and the output side connected to the control input of the switching element.
An object of the invention is achieved by having the first circuit be a logic circuit, by the switching element having a controllable configuration, and by a second logic circuit being connected on the input side to the clock-signal contact and on the output side to the control input of the switching element.
In integrated circuit technology, controllable switching elements are usually configured as transistors and have only a very low forward resistance so that the voltage drop across such a switching element during operation of the data carrier through the contacts is negligible. In addition, the low voltage drop means that lower supply voltages are also possible. According to the invention, the presence of a clock signal is necessary for the conductivity switching of the switching element. A second logic circuit is provided to establish the presence of the clock signal and activate the switching element correspondingly.
In accordance with another feature of the invention, the second logic circuit has a rectifier element for obtaining a supply voltage from the clock signal.
In an advantageous development of the invention, the second logic circuit may be both autonomous, that is, obtain its supply voltage from the clock signal, and be connected to the supply voltage.
Using the clock signal as a criterion for switching through of the supply voltage to the first logic circuit has the advantage that the precondition of the presence of a clock signal is not a restrictive condition. This is true because the first logic circuit would not operate without the clock signal, even if the supply voltage were present. Consequently, a signal that is already necessary is used in an advantageous way as a switching condition.
In accordance with a further feature of the invention, the second logic circuit is connected to the at least one supply-voltage contact.
In accordance with an added feature of the invention, there is provided a voltage regulator having a regulator control input, the voltage regulator being connected upstream of the first logic circuit, the output side of the second logic circuit being connected to the regulator control input.
Contactless operation usually requires a supply voltage regulator because the operating voltage of the data carrier is obtained from the signal received from the coil and the amplitude of the signal can fluctuate considerably due to its dependence on the distance of the data carrier from a transmitter. The regulated voltage is usually lower than the voltage supplied by the contacts. Thus, the regulator would be overloaded when operated with contacts. In a development according to the invention, the output signal of the second logic circuit, detecting the clock signal, is used for deactivating the regulator.
In accordance with a concomitant feature of the invention, the data carrier is a chip card.
Other features that are considered as characteristic for the invention are set forth in the appended claims.
Although the invention is illustrated and described herein as embodied in a data carrier for operation with and without contacts, it is, nevertheless, not intended to be limited to the details shown since various modifications and structural changes may be made therein without departing from the spirit of the invention and within the scope and range of equivalents of the claims.